A group of firefighters watch a fire as they conduct a burnout to clear dry underbrush near a stand of pine trees along Evergreen Road in the Stanislaus National Forest on Aug. 28 near Buck Meadows, Calif. The controlled burning will prevent wildfire flames from crossing the road and threatening nearby structures. Elias Funez, The Modesto Bee, via AP

A column of smoke rises from the Rim Fire on Aug. 28 near Yosemite National Park in California. The wildfire is still burning its way into the huge tourist attraction as thousands of firefighters using planes and bulldozers battle the flames. Mike McMillan, U.S. Forest Service, via AFP/Getty Images

A smoky haze from a huge California wildfire burning more than 150 miles away hangs over Virginia Street in Reno. Most of the Sierra's eastern front from south of Carson City, Nev., to north of Lake Tahoe has been under an air-quality alert for nearly a week. Scott Sonner, AP

Big Bear firefighter Jon Curtis keeps a close eye on a "slop over" fire that jumped State Route 120 just east of Hardin Flat Road while fighting the Rim Fire in the Stanislaus National Forest. Elias Funez, AP

A firefighter monitors a back fire while battling the Rim Fire on Aug. 22 in Groveland, Calif. The Rim Fire is out of control and threatens 2,500 homes outside Yosemite National Park. Justin Sullivan, Getty Images

A burned forest surrounds a home destroyed by a wildfire near Rockport, Utah. The fire, which appears to have been started by lightning, had burned about 400 acres by Aug. 14. Ravell Call, The Deseret News, via AP

Wendy Gray, left, talks with a neighbor as her husband, Mike, right, fields calls from neighbors about their homes and pets that were left behind in Coalville, Utah. A wildfire destroyed 15 homes in Summit County. Leah Hogsten, Salt Lake Tribune, via AP